Recently, a light-emitting diode (hereinafter, referred to as “LED”) has been increasingly used as a light source for a surface light source device of an edge-lit type with a hollow structure without using a light guide plate. In such a surface light source device, there is a case where a combination of an LED and a light flux controlling member (condenser lens) may be used in order to control the distribution of light emitted from the LED (see, for example, PTL 1).
PTL 1 sets forth an illumination apparatus having a square-shaped frame, a pair of light diffusing plates (members to be irradiated) disposed so as to cover opposing openings of the frame, a plurality of LEDs disposed linearly on one internal surface of the frame, and one condenser lens that covers the plurality of LEDs. In the illumination apparatus of PTL 1, the sectional shape of the condenser lens in a direction orthogonal to the arrangement direction of LEDs is the same in any point of the condenser lens. The illumination apparatus set forth in PTL 1 makes the distribution of light emitted from an LED narrower with the condenser lens. In this manner, the illumination apparatus set forth in PTL 1 can illuminate the light diffusing plate unifoimly to some degree by propagating light emitted from an LED farther.